U.S. patent application number 09/893979 was filed with the patent office on 2002-01-24 for receiver.
Invention is credited to Makivuoti, Mauri, Talmola, Pekka.
Application Number | 20020008788 09/893979 |
Document ID | / |
Family ID | 9894881 |
Filed Date | 2002-01-24 |
United States Patent
Application |
20020008788 |
Kind Code |
A1 |
Talmola, Pekka ; et
al. |
January 24, 2002 |
Receiver
Abstract
The present invention relates to receivers such as multi-carrier
receivers. An orthogonal frequency division multiplex (OFDM)
receiver in a terrestrial digital video broadcast (DVB-T) network
is required to operate in a complex channel environment, wherein
high power analogue television signals may co-exist. The mix of
high power analogue television signals and lower power digital
signals results primarily from the concurrent existence of both
analogue and digital television services. Normal network planning
assumes that the adjacent analogue channels can be up to 35 dB
higher than a digital channel. In order to cope with such high
power adjacent channels, and to be able to successfully receive a
desired digital channel, the radio frequency (RF) stages of a
digital receiver must be highly linear. If a digital receiver is
not highly linear, intermediate modulation (IM) products may
interfere with the desired signal and prevent good reception.
However, current RF amplifiers are not completely linear devices,
and exhibit non-linear properties. High linearity can be achieved,
however, by having high bias currents in the RF amplifiers of a
digital receiver. The present invention provides a receiver having
improved power efficiency.
Inventors: |
Talmola, Pekka; (Turku,
FI) ; Makivuoti, Mauri; (Turku, FI) |
Correspondence
Address: |
ANTONELLI TERRY STOUT AND KRAUS
SUITE 1800
1300 NORTH SEVENTEENTH STREET
ARLINGTON
VA
22209
|
Family ID: |
9894881 |
Appl. No.: |
09/893979 |
Filed: |
June 29, 2001 |
Current U.S.
Class: |
348/732 ;
348/E5.096; 348/E5.108; 455/234.1 |
Current CPC
Class: |
H04N 5/4401 20130101;
H04N 21/41407 20130101; H04N 21/426 20130101; H04N 5/44 20130101;
H04N 21/4436 20130101; H04N 21/6112 20130101; H04N 21/44209
20130101 |
Class at
Publication: |
348/732 ;
455/234.1 |
International
Class: |
H04B 001/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 30, 2000 |
GB |
0016249.5 |
Claims
What is claimed is:
1. A receiver for receiving signals conveying information, wherein
the receiver includes a non-linear element, the receiver
comprising: a demodulator for demodulating the received signal to
produce demodulated information; means for determining the quality
of the demodulated information; and means for adjusting the
linearity of the non-linear element in dependence on the determined
quality.
2. A receiver according to claim 1, wherein the non-linear element
is a radio frequency (RF) amplifier for amplifying the received
signals.
3. A receiver according to claim 1 or 2, wherein the means for
determining the quality is a forward error correction (FEC)
unit.
4. A receiver according to claim 3, wherein the FEC further
provides a bit error rate (BER).
5. A receiver according to any of claim 2, 3 or 4, wherein the
means for adjusting the linearity comprises a controller capable of
adjusting the bias current applied to the RF amplifier.
6. A receiver according to claim 5, wherein the controller adjusts
the bias current applied to the RF amplifier based on an
instantaneous value of BER.
7. A receiver according to claim 5 or 6, wherein the controller
adjusts the bias current applied to the RF amplifier based on an
average of a plurality of BER values.
8. A receiver according to any preceding claim, adapted for
receiving multi-carrier signals.
9. A receiver according to any preceding claim, adapted for
receiving orthogonal frequency division multiplex (OFDM)
signals.
10. A portable terminal comprising a receiver as claimed in any
preceding claim.
11. A method of receiving signals conveying information at a
receiver comprising a non-linear element, the method comprising:
demodulating the received signal to produce demodulated
information; determining the quality of the demodulated
information; adjusting the linearity of the non-linear element in
dependence on the determined quality.
12. A method according to claim 11, further comprising comparing
the determined quality with a first predetermined value, and
increasing the linearity of the non-linear element when the
determined quality is less than the first predetermined value.
13. A method according to claim 11 or 12, further comprising
comparing the determined quality with a second predetermined value,
and decreasing the linearity of the non-linear element when the
determined quality is greater than the second predetermined
value.
14. A method of receiving signals conveying information at a
receiver comprising a non-linear element, the method comprising:
demodulating the received signal to produce demodulated
information; determining the quality of the demodulated
information; and comparing the determined quality with a first
predetermined value, and increasing the linearity of the non-linear
element when the determined quality is less than the first
predetermined value and comparing the determined quality with a
second predetermined value, and decreasing the linearity of the
non-linear element when the determined quality is greater than the
second predetermined value.
15. A receiver as substantially herein described with reference to
the accompanying drawing.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to receivers such as
multi-carrier receivers.
[0002] An orthogonal frequency division multiplex (OFDM) receiver
in a terrestrial digital video broadcast (DVB-T) network is
required to operate in a complex channel environment, wherein high
power analogue television signals may coexist. The mix of high
power analogue television signals and lower power digital signals
results primarily from the concurrent existence of both analogue
and digital television services.
[0003] FIG. 1 shows an example of a typical section of the UHF
spectrum, showing a number of adjacent channels N-1, N and N+1,
with each channel occupying 8 MHz bandwidth. The existing analogue
channels are distributed in the UHF spectrum according to known
frequency planning criteria. Due to the nature of analogue receiver
technology, especially when analogue television was first
introduced, and the difficulty of achieving adequate channel
interference rejection, each analogue channel is separated from the
others by a minimum gap of 8 MHz. It is in these gaps that digital
channels are broadcast.
[0004] FIG. 2 is a block diagram showing a digital video
broadcasting (DVB-T) set-top-box receiver 200 according to the
prior art. A DVB-T signal is received by an antenna 202. The
received signal is amplified by a radio frequency (RF) amplifier
204. The amplified signal is subsequently mixed in a mixer 206 with
a signal generated by a local oscillator 214. The mixer 206 reduces
the frequency of the received RF signal to that of an intermediate
frequency (IF) signal. The IF signal is amplified by an IF
amplifier 208, before passing to a demodulator 209 and a forward
error corrector (FEC) 210, where demodulation of the signal and
error correction takes place. The output 212 from the FEC 210 is a
DVB-T transport stream.
[0005] Normal network planning assumes that the adjacent analogue
channels can be up to 35 dB higher than a digital channel. In order
to cope with such high power adjacent channels, and to be able to
successfully receive a desired digital channel, the radio frequency
(RF) stages of a digital receiver must be highly linear. If a
digital receiver is not highly linear, intermediate modulation (IM)
products may interfere with the desired signal and prevent good
reception. However, current RF amplifiers are not completely linear
devices, and exhibit non-linear properties. High linearity can be
achieved, however, by having high bias currents in the RF
amplifiers of a digital receiver.
SUMMARY OF THE INVENTION
[0006] According to a first aspect of the present invention, there
is provided a receiver for receiving signals conveying information,
wherein the receiver includes a non-linear element, the receiver
comprising: a demodulator for demodulating the received signal to
produce demodulated information; means for determining the quality
of the demodulated information; and means for adjusting the
linearity of the non-linear element in dependence on the determined
quality.
[0007] This advantageously allows the power consumption of
receivers to be reduced in certain conditions. As people become
more environmentally aware, efficient and economic consumer goods
becomes increasingly important. Such reductions in power
consumption can contribute significantly to power savings for the
consumer. The present invention provides further advantages in the
field of mobile and portable receivers, wherein reductions in power
relates directly to increased operating time from a given battery
or portable power unit or can even result in a reduction in size of
a battery unit.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The invention will now be described, by way of example only,
with reference to the accompanying diagrams in which:
[0009] FIG. 1 is a diagram showing a typical portion of the UHF
spectrum;
[0010] FIG. 2 is a block diagram showing a digital video
broadcasting (DVB-T) receiver according to the prior art;
[0011] FIG. 3 is a block diagram showing a digital video
broadcasting (DVB-T) receiver according to an embodiment of the
present invention;
[0012] FIG. 4 is a graph showing the relationship between bias
current and linearity; and
[0013] FIG. 5 is a flow diagram showing an example of the
functional steps made by the controller of FIG. 3.
DETAILED DESCRIPTION OF THE INVENTION
[0014] As described above, FIG. 1 is a diagram showing a typical
portion of the UHF spectrum, showing a digital COFDM channel
sandwiched between adjacent analogue television channels. Depending
on the exact location within the UHF spectrum, the digital channel
may be bound on one or both sides by an adjacent analogue
television signal. It may also be possible for a digital channel to
exist without any immediate neighbours. This will, however, depend
on the precise location within a frequency band. The worse case
scenario is where the digital channel is bounded by an adjacent
analogue television channel on both sides.
[0015] The linearity of an RF amplifier is governed by the amount
of bias current applied thereto. FIG. 4 is a graph showing the
relationship between bias current and linearity. It is clear that
increased bias current results in increased linearity.
[0016] FIG. 3 is a block diagram showing a terrestrial digital
video broadcasting (DVB-T) receiver according to an embodiment of
the present invention. The receiver may be a fixed consumer
set-top-box type receiver, or alternatively may be a portable or
mobile receiver. The receiver functions largely as described above
with reference to FIG. 2, with the addition of a feedback loop and
a controller 318. Although the detail of RF amplifier 204 of FIG. 2
and 304 of FIG. 3 has not been shown, it will be apparent to those
skilled in the art that a wide variety of standard RF amplifying
techniques could be used, including field effect transistors (FET),
and power integrated circuits (ICs).
[0017] The controller 318 acquires the bit error rate (BER) which
is generated by the FEC 310. The BER is available on most
commercially available FECs and may be supplied directly as an
output signal, or it may be readable from an internal or an
external memory. The BER gives an indication of the number of
errors on the decoded signal. Typically, BER is only used during
installation of a receiver where it greatly assists correct
alignment of the antenna. For example, if the antenna is not
correctly aligned, noise on the received signal will cause errors
to be created in the decoded signal. By displaying BER, for example
as a bar graph on an installation screen, a user may orient the
antenna to achieve the lowest BER.
[0018] The controller 318 adjusts the bias current of the RF
amplifier in accordance with the BER. FIG. 5 is a flow diagram
showing an example of the functional steps made by the controller
of FIG. 3.
[0019] When the receiver is tuned to a new channel (step 500), the
controller 318 sets the bias current of the RF amplifier 304 to the
highest level to ensure the highest linearity (step 502). Once the
receiver has locked to the channel and has started decoding the
received signal (step 504), the controller 318 acquires the BER
from the FEC 310 (step 506). The controller 318 monitors the BER to
determine whether the BER is better than a predetermined acceptable
level (step 508). If the BER is better than the predetermined
acceptable level, the controller 318 reduces the bias current
applied to the RF amplifier 304 (step 510). If the BER is worse
than a second predetermined acceptable level (step 512) the
controller 318 increases the bias current (step 514) to attempt to
bring the BER up to an acceptable level. In this way, the BER may
be maintained within two acceptable limits. In an alternative
embodiment, the controller may have only one threshold level,
whereby the controller makes adjustments to the bias current to
keep the BER as close to the threshold value as possible. A
typically minimum acceptable BER threshold is around
2.times.10.sup.-4, which results in a quasi-error free transport
stream (having an error rate <1.times.10.sup.11). If the BER is
better (i.e. less) than this value there will be no visible errors
in a decoded picture. It is however preferable to set the
acceptable threshold above the minimum required threshold, to allow
for worst case scenarios.
[0020] By adjusting the bias current for the RF amplifier 306, it
is possible to reduce the power consumption of the receiver, where
conditions allow, without affecting the integrity of the decoded
signal.
[0021] In receivers according to the prior art, maximum bias
current is used at all times. Such receivers are therefore are not
power efficient, especially when conditions dictate that bias
current can be successfully reduced without affecting the integrity
of the decoded signal.
[0022] In one embodiment of the present invention, the measurement
of the BER is taken as an instantaneous value. In a further
embodiment of the present invention, the BER value is averaged over
a period of time. Taking instantaneous values of BER may, however,
lead to excessive bias current adjustments being made, whereas
averaging the BER values over too long a time period may not enable
the system to react quick enough to changes in the received signal
quality. In yet a further embodiment, the controller adjusts the
bias current based on either an instantaneous value of BER or on an
average value of BER, depending on the specific circumstances. For
example, in a fixed set-top-box receiver, the channel conditions
are unlikely to change quickly, therefore it may be preferable to
average the BER values over a period ranging from a number of
cycles up to around 10 seconds. In a mobile or portable receiver,
where channel conditions may vary rapidly, using the instantaneous
value of BER may be preferable.
[0023] In yet a further embodiment of the present invention, the
controller adjusts the bias current based on the number of corrupt
carriers which are detected, rather than on the BER value.
[0024] In yet another embodiment, for example, with terminals which
are moved to a new location infrequently, such as for an exhibition
or conference etc, it may be advantageous to perform the bias
current adjustments less often, since the reception characteristics
are less likely to change frequently.
[0025] It will be understood by those skilled in the art, that many
variations on the above could be made without detracting from the
inventive concepts of the present invention. For instance, the bias
current could also be adjusted in accordance with any other
variable which gives an indication of the quality of the received
or the decoded signal. Furthermore, the bias current could be
adjusted on any other component of which bias current affects
linearity, such as mixers, further amplifiers etc. Indeed, the
controller could be adapted to control the bias current of a
plurality of devices of which bias current affects linearity.
[0026] Although the present invention is herein described with
reference to digital transmissions, those skilled in the art will
also appreciate that the present invention can be equally applied
to analogue reception--providing that a measure of the quality of
the received signal can be obtained, and the quality of the
received signal can be influenced by a controllable non-linear
element.
* * * * *